DE10027345B4 - Monopulse radar - Google Patents

Monopulse radar

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Publication number
DE10027345B4
DE10027345B4 DE2000127345 DE10027345A DE10027345B4 DE 10027345 B4 DE10027345 B4 DE 10027345B4 DE 2000127345 DE2000127345 DE 2000127345 DE 10027345 A DE10027345 A DE 10027345A DE 10027345 B4 DE10027345 B4 DE 10027345B4
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Germany
Prior art keywords
monopulse
radar
angular direction
antennas
ar8
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Expired - Lifetime
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DE2000127345
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German (de)
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DE10027345A1 (en
Inventor
Hiroshi Hazumi
Hiroaki Kumon
Kazuma Natsume
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Denso Corp
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Denso Corp
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Priority to JP15646799 priority Critical
Priority to JP11-156467 priority
Priority to JP2000063635A priority patent/JP4258941B2/en
Priority to JP63635/00 priority
Application filed by Denso Corp filed Critical Denso Corp
Publication of DE10027345A1 publication Critical patent/DE10027345A1/en
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Publication of DE10027345B4 publication Critical patent/DE10027345B4/en
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/06Systems determining position data of a target
    • G01S13/46Indirect determination of position data
    • G01S13/48Indirect determination of position data using multiple beams at emission or reception
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/06Systems determining position data of a target
    • G01S13/42Simultaneous measurement of distance and other co-ordinates
    • G01S13/44Monopulse radar, i.e. simultaneous lobing
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01SRADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/87Combinations of radar systems, e.g. primary radar and secondary radar

Abstract

Radar device comprising: a transmitter (4) which transmits a radar wave; a signal receiver (6) with antennas (AR1-AR8), which form overlapping antenna lobes, in order to define monopulse areas, the signal receiver (6) being designed such that it can receive an echo of the radar wave from a target object in the monopulse areas, to generate a pair of input signals; an angular direction data determination circuit (10) configured to process the pair of input signals generated per monopulse area to obtain angular direction data in a time sequence, each of which provides an angular direction of the target object based on amplitude or phase differences between the two per monopulse area Display input signals; and a change determination circuit (10) configured to determine a change in the angular direction data obtained in a time sequence in each of the monopulse areas and determine the angular direction data whose change is within a preselected allowable range as values which when determining an angular direction of ...

Description

  • Background of the invention
  • 1. Technical field of the invention
  • The present invention relates generally to a monopulse radar device designed to determine the azimuth of a target, and more particularly to an improvement of such a monopulse radar device which is capable of discriminating between targets located near each other within a radar detectable zone Accuracy is suitable.
  • 2. State of the art
  • Self-propelled radar systems are known, which are designed to control a target object such as an obstacle or a preceding vehicle for a tempo control and / or an anti-collision control. It is important for such self-propelled radar systems to obtain azimuth data for determining a precise positional relationship between a vehicle on which a radar device is mounted and a target as well as the distance to the target and the relative speed of the target. This is achieved, for example, with beam scan systems or monopulse systems. The like in 11 (a) The beam scanning systems shown measure levels of echoes from radar waves whose directivity differs from each other to receive a received signal level distribution as in FIG 11 (b) and select one of the radar reflections whose signal level in the distribution is greatest, as indicated by the azimuth or the angular direction of a target object. In the 12 (a) The monopulse systems shown receive radar echoes simultaneously through a pair of receiving antennas a and b which are slightly spaced apart (by a distance D in the figure) to determine a phase difference between the received signals resulting from the difference of the distance d (= D · Sinθ) of the radar reflections which have traveled a distance when the angle defined by the incident direction of each of the radar reflections with a line perpendicular to a front plane of the received antennas a and b is defined as θ or from one Amplitude difference between the received signals (see. 13 (a) and 13 (b) ), which results from a difference of the radiation or Strahlungskeulenrichtfähigkeit the received antennas.
  • It is possible for the monopulse systems to accurately measure the azimuth of the target object only in an area where lobes of two antennas overlap with each other (referred to below as a monopulse area). Thus, some of the monopulse systems increase a detection range using more than three receiving antennas arranged such that two adjacent receiving antennas form the monopulse range for measuring the azimuth. For example, the first ones teach Japanese Patent Publication No. 9-152478 and 62-259077 such systems.
  • An improvement in the measurement accuracy of the azimuth in the beam scanning systems requires the formation of fine beams, thereby requiring an increase in the size (i.e., an aperture) of the antennas.
  • However, when the beam scanning systems are used as a self-propelled radar, the mounted antennas are limited in size, which can lead to the difficulty of obtaining a desired measurement accuracy.
  • The monopulse systems have a drawback in that when a plurality of targets are at the same interval from a radar-mounted vehicle, as when two automobiles are side by side before radar. driven vehicle, an error in the measurement of the azimuth is caused. In particular, when two automobiles travel in parallel at substantially the same speed, radar reflections from the two automobiles having substantially the same frequency are received by the monopulse system as a compound wave. Usually millimeter waves are used in a self-propelled radar. The wavelength of a radar reflection will thus be on the order of a few mm, so that the phase of the radar reflection will change greatly even if the distance to the target changes in units of millimeters.
  • When two target automobiles travel side by side, but only one of them is located within a monopulse range (at a position as indicated by ➀ in a graph of FIG 14 (a) displayed), a radar wave (ie, a vector as indicated by a broken line) reflected from the one of the target automobiles in the monopulse range and a radar wave (ie, a vector as indicated by a solid line ➁) different from the one other target automobile, which is outside the monopulse range (at a position as represented by ➁ in the graph), with respect to the signal level when receiving from the monopulse system, so that a composite wave (ie, a vector as indicated by a solid line) at which the two reflected radar waves are mixed will approach the radar wave which is from the Target automobile is reflected within the monopulse range, thereby making it possible to obtain accurate information about the azimuth. If, however, two automobiles like in 14 (b) both located within the monopulse range, the radar waves (vectors as indicated by dashed lines ➀ and ➁) reflected by the two automobiles and received by the monopulse system have substantially the same signal level, so that a composite wave thereof (FIG. that is, a vector as indicated by a solid line) shows the directions that are greatly different from the angular directions of the target automobiles. This causes only one of the target automobiles to be detected.
  • Specifically, in the monopulse system, radar waves reflected from a pair of targets which are within the same monopulse range are mixed in one vector to form a composite wave which is different in phase and amplitude from both reflected radar waves It is difficult to measure the azimuth of the targets using the phase and the amplitude of the reflected radar wave.
  • From the EP 0 766 100 A1 1 is a radar apparatus with a transmitter which transmits radar waves and a signal receiver with antennas which form overlapping antenna lobes to define a monopulse range. The signal receiver is configured to receive an echo of the radar wave from a target object in the monopulse regions to produce a pair of input signals. Further, the radar apparatus has an angular direction data determining circuit which processes the one-pulse-per-pixel pair of input signals to obtain angular direction data in a time sequence each indicating an angular direction of the target object based on amplitude or phase differences between the two input signals per monopulse range.
  • Summary of the invention
  • It is an object of the present invention to obviate the drawbacks of the prior art and, more particularly, to provide a radar apparatus capable of discriminating against two targets located near to each other for measuring angular directions thereof with high accuracy.
  • The object is achieved by providing a radar device according to claim 1.
  • According to one aspect of the invention, there is provided a radar apparatus comprising: (a) a transmitter which transmits a radar wave; b) a signal receiver having antenna lobes overlapping each other to define a plurality of monopulse regions, the signal receiver receiving an echo of the radar wave from a target object in each of the monopulse regions to produce a pair of input signals; (c) an angular direction data determining circuit which processes the input signals generated in each of the monopulse regions to obtain angular direction data in a time sequence each indicating an angular direction of the target object based on differences in amplitude or phase between components of the input signals; and (d) a change determination circuit that determines a change in the angular direction data obtained in a time sequence in each of the monopulse areas. If the change is within a preselected permissible range, the change determiner determines its angular direction data as effective in accurately determining an angular direction of the target object.
  • For example, when two target vehicles ride side by side in front of a radar-mounted vehicle, the radar receives a mixture of radar reflections of a radar wave from target vehicles in the monopulse range. This blended radar reflection differs in phase and amplitude from each of the radar reflections from the target vehicles and varies greatly with a slight change in the distance between the radar-tagged vehicle and the target vehicles, resulting in a large change in azimuth caused by cyclic monitoring the mixed radar reflection is measured. The radar apparatus of this invention thus monitors in time the azimuth data in each of the monopulse areas and ignores some of the azimuth data whose temporal change is outside an allowable range when the angular direction of each target is determined, thereby improving the stability and reliability of the control using the azimuth data is improved.
  • According to the preferred embodiment of the invention, the signal receiver for providing the antenna lobes is designed such that two adjacent monopulse regions partially overlap. It is also advisable that the monopulse ranges overlap so that radar reflections from two vehicles traveling side by side at the same interval can be received by the radar-mounted vehicle at different signal levels whose difference magnification is greater than a preselected reference value.
  • The signal receiver includes three or more receive antennas located with the antenna lobes aligned in different directions, respectively, and two adjacent antenna lobes defining one of the monopulse regions.
  • The signal receiver may include a plurality of receiving antennas arranged in a line so that antenna lobes thereof are aligned in the same direction, and a signal processing circuit summing outputs from the receiving antennas with a given direction to form the beams. In this case, the signal processing circuit may be formed to include a so-called phased array antenna structure that includes a phase shifter that outputs the phase of the antenna to weight the antenna outputs and an adder that outputs the outputs of the phase shifter together , or an analog-to-digital converter which samples the outputs of the receiving antennas to produce digital signals, and an arithmetic circuit which performs a complex Fourier transform on the digital signals in space series along an array of the receiving antennas , whereby the so-called digital beams or radiation lobes are formed.
  • The arithmetic circuit may add null strobe signals to the digital signals generated by the analog-to-digital converter to increase the number of signals to simultaneously experience the complex Fourier transform greater than the number of outputs from the receive antennas. This technique is called "zero-padding," which is taught, for example, in Chapter 11 Irregular Vibration and Spectrum Analysis, published by the Ohm Company. In particular, adding the beacon signals causes the number of receive antennas to logically increase, thereby increasing the number of antenna lobes within the radar detectable zone, thereby increasing the accuracy of the azimuth measurement of the target.
  • When a plurality of targets are located within the radar detectable zone at substantially the same distance from the radar, the formation of the monopulse regions, with two adjacent monopulse regions partially overlapping, enables effective azimuth data with respect to the same target to be obtained in some of the monopulse regions , Assuming that two adjacent ones of nine monopulse areas M1 to M9 as in 15 (a) when three-quarters (3/4) of them overlap and two targets T1 and T2 are present, the monopulse areas M2 to M4 detect only the destination T1. The monopulse regions M5 and M6 detect both targets T1 and T2, but it is impossible to accurately measure the azimuth thereof since radar reflections of a radar wave are received by the targets T1 and T2 at substantially the same signal levels. The monopulse areas M7 to M8 receive only the destination T2. Monopulse areas M1 and M9 do not detect targets. Specifically, the azimuth data of one of the targets T1 and T2 is obtained from two or more of the monopulse regions M1 to M9.
  • Assuming that two out of seven monopulse ranges M1 to M7 are as in 14 (b) shown overlapped with respect to a half (1/2) thereof and that the width of the targets T1 and T2 is greater than half the width of each of the monopulse regions M1 to M7, the monopulse regions M2 and M3 detect only the target T1. The monopulse region M4 detects the targets T1 and T2, but it is not possible to accurately measure the azimuth thereof because the radar reflections of a radar wave are received by the targets T1 and T2 at substantially the same signal levels. The monopulse areas M5 and M6 capture only the target T2. Monopulse areas M1 and M7 do not detect targets. Specifically, the azimuth data with respect to one of the targets T1 and T2 is obtained from two or more monopulse regions M1 to M7.
  • In the above cases, the radar apparatus may include: (a) a transmitter which transmits a radar wave; (b) a signal receiver that provides antenna lobes that overlap each other to define a plurality of monopulse regions, the signal receiver receiving an echo of the radar wave from a target object in each of the monopulse regions to produce a pair of input signals; (c) an angular direction data determining circuit which processes the input signals formed in each of the monopulse regions to obtain angular direction data each indicating an angular direction of the target object based on differences in amplitude or phase between components of the input signals; and (d) a grouping circuit which, when some of the angular direction data within a given range are close to each other, forms a group including the angular direction data close to each other within the given range; and (e) a determining circuit that effectively determines the angular direction data in the group as values in determining an angular direction of the target object.
  • Brief description of the figures
  • The present invention can be understood from the detailed description given below and from the accompanying figures of the preferred embodiments of the invention are understood which do not serve to limit the invention to specific embodiments but only for explanation and understanding.
  • 1 Fig. 10 is a block diagram showing a radar apparatus of the first embodiment of the invention;
  • 2 (a) represents monopulse areas which are defined by antenna lobes of receiving antennas;
  • 2 B) FIG. 4 shows an explanation representing as vector outputs of receiving antennas, which radar reflections of in 2 (a) present goals;
  • 3 shows a flowchart of a program for determining the azimuth of a target;
  • 4 shows an example of azimuth data obtained by radar reflections of monopulse areas when two automobiles are traveling side by side;
  • 5 Fig. 10 is a block diagram showing a radar apparatus of the second embodiment of the invention;
  • 6 Fig. 10 is a flow chart of a program for determining the azimuth of a target in the second embodiment;
  • 7 Fig. 10 is a flow chart of a program for determining the azimuth of a target in a radar apparatus of an illustrative example which does not form the subject of the invention;
  • 8th FIG. 16 shows an example of azimuth data obtained from radar reflections of monopulse regions in the example of FIG 7 be obtained when two automobiles ride side by side;
  • 9 Fig. 10 is a flow chart of a program for determining the azimuth of a target of the third embodiment;
  • 10 Fig. 13 shows an example of the azimuth data obtained by radar reflections of monopulse areas in the fourth embodiment when two automobiles are driven side by side;
  • 11 (a) shows a conventional radiation beam scanning radar system;
  • 11 (b) provides a distribution of levels of receive antenna outputs in the in 11 (a) represented system;
  • 12 (a) and 12 (b) show illustrative views illustrating the principles of a conventional monopulse radar system;
  • 13 (a) represents levels of outputs of receive antennas in a conventional monopulse radar system;
  • 13 (b) represents a difference in the level of in 13 (a) represented outputs;
  • 14 (a) and 14 (b) Fig. 11 are explanatory views illustrating a difficulty encountered in a conventional monopulse radar system;
  • 15 (a) FIG. 12 illustrates an illustrative example of monopulse regions formed by a radar device not embodying the invention; FIG. and
  • 15 (b) FIG. 10 illustrates an example of monopulse regions formed by a radar device of the invention.
  • Description of the Preferred Embodiments
  • Corresponding to the figures, in which like reference numerals for similar parts are used in several views, in particular correspondingly 1 , becomes a self-propelled radar device 2 of the first embodiment of the invention, which can be used in self-propelled anti-collision or radar cruise control systems to detect the presence of obstacles in front of a radar-mounted vehicle.
  • The radar device 2 generally contains a transmitter 4 , a two-channel receiver 6 , an A / D converter circuit 8th and a microcomputer 10 ,
  • The transmitter 4 sends a radar wave in the form of a millimeter wave via a transmitting antenna AS. An echo of the radar wave or a radar reflection wave (also referred to below as a reflected wave) from a target such as a forward vehicle or an obstacle located on a road is received by eight receiving antennas AR1 to AR8 which are arranged in a line at regular intervals. The recipient 6 mixes signals received from two adjacent receive antennas AR1 to AR8 with one from the transmitter 4 supplied local signal L to beat signals (beat signals) 31 and 32 to create. The A / D converter circuit 8th consists of a pair of A / D converters AD1 and AD2 which receive the beat signals B1 and B2 from the receiver 6 cyclically scans to digital signals D1 and D2 (below also referred to as digital beat signals). The microcomputer 10 performs given operations on the digital heterodyne signals D1 and D2 generated by the A / D converter circuit 8th which will be discussed in detail later.
  • The receiving antennas AR1 to AR8 have mutually different directivity. Two adjacent antennas ARi and ARi + 1 (i = 1, 2, 3, ... 7) of the receiving antennas AR1 to AR8 partially overlap in radiation patterns or lobes to form an overlapping lobe (also referred to below as monopulse region Mi) , In the following discussion, a portion of each monopulse range where a difference between signal levels at any two locations spaced apart at an angle interval of 4 degrees is always greater than 15 dB is referred to as a parallel motion detection zone (ie, a zone which differs from the center line of each monopulse region is shifted in either the right or the left direction by an angle of 2.5 degrees in this embodiment). The receiving antennas AR1 to AR8 are arranged such that the monopulse areas M1 to M7 are formed at intervals of 2.5 degrees or less to define the parallel motion detecting zones which continue to run away from each other without any separation. The transmission antenna AS has the radiation beam width, which covers all monopulse regions M1 to M7.
  • When a maximum radar detection area is 50 m and the width of a lane of a road is 3.5 m, each of the reception antennas AR1 to AR8 is designed with respect to the characteristic of the lobe thereof such that a difference in signal level between any point within the monopulse area and a point which is defined at an interval of four degrees away from the point within the monopulse range is 15 dB or more for detecting automobiles which are side by side with an interval of the lane width (equivalent to an angle of 4 degrees) away from each other with an error of Drive 0,5 m, d. H. in about half the width of automobiles (equivalent to an angle of 0.5 degrees).
  • Specifically, when levels of signals formed by the reception of a target car-reflected radar wave within the monopulse region M1 (referred to below as the on-vehicle ➀) through two of the receiving antennas AR1 to AR8 are paired to form the monopulse region M1 are defined as V1a and VIb, and levels of signals formed by receiving a radar wave reflected by a second target vehicle which is within the monopulse range (hereinafter referred to as in-range vehicle) are defined as V2a and V2b by the same receiving antennas , Va and Vb of composite signals formed by mixing the reflected waves in one of the receiving antennas into a vector in 2 B) expressed. 2 B) Fig. 10 illustrates the case where differences between the levels V1a and V1b originating from the on-vehicle ➀ and the levels Va and Vb of the composite signals respectively show maximum values, ie, phases of the signals constituting one of the composite signals , are aligned perpendicular to each other. In the following discussion, it is assumed that | V1a | = | V1b | = | V1 | and | V2a | = | V2b | = | V2 | applies.
  • How out 2 (a) it can be seen that the phase of the wave generated by a mixture of the radar waves reflected by the vehicle ➀ in the area and the vehicle ➁ located in the area zwischen between two neighboring receiving antennas is shifted by a maximum of tan -1 (| V2 | / | V1 |) , A shift of the phase difference Δθy between the signals received from the paired reception antennas is thus expressed by the equation (1) below. Δθy = 2 × ton -1 (| V2 | / | V1 |) (1)
  • For example, in a case where the azimuth is measured using the phase difference monopulse technique, the azimuth angle θx is determined with a one-to-one correspondence to the phase difference θy. A conversion ratio of the phase difference θy to the azimuth angle θx is determined such that an error of the azimuth determination is minimized. For example, when the monopulse range is defined by about 5 degrees, the spaces between the receiver antennas are determined such that the conversion ratio is set to about 40 as shown below in equation (2). θy = 40 × θx + θc (2) where θc is a constant.
  • From equation (2), the relationship between the azimuth angle error Δθx and the phase shift difference Δθy can be given by equation (3). Δθy = 40 × Δθx (3)
  • Substituting equation (1) into equation (3) yields | V2 | / | V1 | = tan (20 · Δθx) (4)
  • From equation (4), it can be seen that decreasing the azimuth angle error Δθx to below 0.5 degrees reduces the level V2 of the signal formed by the wave reflected from the in-range vehicle ➀ to below the level V2 of the signal which is formed by the wave reflected from the on-vehicle ➁, minus 15 dB or more.
  • In order to 1 come back, the transmitter consists of a high-frequency oscillator 12 and a distributor 14 , The high frequency oscillator 12 generates a high-frequency signal in a millimeter band, which is modulated to change with a time similar to a triangular wave. The distributor 14 with respect to the energy splits that from the high-frequency oscillator 12 formed high-frequency signal in the transmission signal Ss and the local signal L. The transmission signal Ss is radiated from the transmission antenna As as a radar wave. The local signal L becomes the receiver 6 fed.
  • The recipient 6 has two channels: a first channel ch1 which includes a selector SEL1, a mixer MX1 and an amplifier AMP1, and a second channel which includes a selector SEL2, a mixer MX2 and an amplifier AMP2. The selector SEL1 is responsive to a select signal S1 from the microcomputer 10 is output to select one of the receiving antennas AR1, AR3, AR5 and AR7 to send a signal Sr1 received from one of the receiving antennas AR1, AR3, AR5 and AR7 to the mixer MX1. The mixer MX1 mixes the signal Sri with the local signal L to generate the beat signal B1, which is a frequency component equivalent to a difference of the signal Sr1 and the local signal L. The amplifier AMP1 amplifies the beat signal B1 and gives it to the A / D converter circuit 8th out. The second channel ch2 differs from the first channel only in that the selector SEL2 is responsive to a selection signal S2 received from the microcomputer 10 is output to select one of the receiving antennas AR2, AR4, AR6 and AR8 to send a signal Sr2 received from one of the receiving antennas AR2, AR4, AR6 and AR8 to the mixer MX2. Other operations are identical and a detailed description thereof is omitted here.
  • Each amplifier AMPj (j = 1, 2) is also designed such that a filtering function is performed to remove unwanted high frequency components from the beat signal Bj.
  • The microcomputer 10 is formed of a CPU, a ROM and a RAM and has an input port in which data from the A / D converter circuit 8th an output port which outputs the wave signals S1 and S2 and a digital signal processor DSP which is used to perform a fast Fourier transform (FFT). In particular, the microcomputer generates 10 the wave signals S1 and S2 to switch between the starting antennas AR1, AR3, AR5 and AR7 and between the receiving antennas AR2, AR4, AR6 and AR8 sequentially and in synchronization with a frequency modulation cycle of the transmission signal Ss, and performs an azimuth determination operation to determine the azimuth or the Angle direction of a target object based on samples D1 and D2 of the beat signals B1 and B2 (also referred to as digital beat signals Dj below) which are respectively obtained in one of the first and second channels ch1 and ch2.
  • In operation, when the radar wave in the form of a frequency modulated undamped wave (FM-CW) from the transmitting antenna AS of the transmitter 4 is sent and the antennas AR1 to AR8 of the receiver 6 receive each echo of the radar wave, each receiver channel chj mixes by the mixer MXj the input signal Srj formed by the antenna ARj with that of the transmitter 4 supplied local signal L to generate the beat signal Bj formed of a frequency component equivalent to a difference in frequency between the input signal Srj and the local signal L amplifies and removes unwanted high frequency components from the beat signal Bj by the amplifier AMPj and converts the beat signal Bj the A / D converter ADj in the digital beat signals Dj. Each A / D converter ADj is designed to change the beat signal Bj M-times (M = 512 in this embodiment) every half-cycle periodically with respect to the frequency of the transmission signal Ss, that is, every time the frequency of the transmission signal Ss modulates is used to increase or decrease linearly. In the following discussion, a period of time during which the frequency of the transmission signal Ss is modulated to be linearly ramped is called a modulated-frequency rising range, while a period of time during which the frequency of the transmission signal Ss is so modulated For example, a linear decay is referred to as a modulated-frequency falling range.
  • 3 Fig. 10 is a flow chart of one of the microcomputer 10 program to determine the azimuth or angular direction of an object within the radar detection zone. This program is executed each time the receiving antennas AR1 to AR8 have all been selected, in other words, the A / D converter circuit 8th stores the samples D1 and D2 which are formed by sampling the beat signals Bj for one cycle of frequency changes in the transmission signal Ss formed by the signals Srj obtained with respect to all the seven monopulse areas M1 to M7 respectively through two adjacent reception antennas AR1 to AR8 To be defined.
  • After the program has started, the routine goes to the step 110 in which an ID number i is initialized to one (1) for identification of one of the monopulse areas Mi.
  • The routine goes to the step 120 in which a real operation of a Fourier transform (referred to below as time series FFT operation) is performed in a time sequence using the fast Fourier transform technique with respect to each series of samples D1 and D2 which are in a cycle of frequency changes in the transmission signal Ss are obtained from the input signals Srj formed in the first and second channels ch1 and ch2 by echoes of a radar wave received in one of the monopulse regions M1 to M7 (ie, in the monopulse region Mi) indicated by the ID Number i is called.
  • The program goes to the step 130 in which the peak of frequency components in each of the first and second channels ch1 and ch2 are obtained from results of the time series FFT operation in the step 120 is extracted to determine the frequency of the beat signal Bj and the phase or amplitude (ie, signal strength) of a frequency component of the beat signal Bj. The routine continues with the step 140 in which the frequency components obtained in the first and second channels ch1 and ch2 are grouped, and a phase difference or an amplitude difference between the frequency components in each group is determined.
  • The routine continues with the step 150 at which azimuth data indicative of the azimuth or the angular direction of the target object, from that in the step 140 obtained phase or amplitude differences are obtained using the known phase monopulse or amplitude monopulse techniques. The azimuth data may be obtained in each cycle of the program using a mathematical equation or lookup using a phase difference (or amplitude difference) to azimuth translation table stored in the microcomputer 10 preinstalled.
  • The routine continues with the step 160 in which an identity check operation is performed for determining whether the target object detected in this program is identical to one detected in a previous program cycle in which an echo of a radar wave is processed by the same monopulse region Mi. This determination can be made on the basis of the following fact. The speed of movement of the target object is limited, and the relative velocity of the radar-mounted vehicle and the target vehicle and the distance to the target object usually change in a limited range as a function of a cycle in which data from echoes of radar waves from the same monopulse range Mi to be won. A frequency change will thus be within a limited range if the targets are identical to each other.
  • The program moves to the step 170 in which the results of the surgery in the step 160 be analyzed to determine whether the target object detected in this program cycle is new or not. If the answer is YES, the program goes directly to the step 210 continued. Alternatively, if the answer NO is obtained, meaning that the target object detected in this program cycle is identical to one detected in the previous program cycle, then the routine goes to the step 180 Next, in which a determination value .DELTA.V for determining a time-sequential change of the thus obtained azimuth data is calculated. The program moves to the step 190 in which it is determined whether or not the change determination value ΔV is larger than a change threshold ΔVth. The change determination value ΔV may be an average value of azimuth angles measured in the last N program cycles including this program cycle, or a deviation thereof.
  • If in the step 190 the answer YES is obtained, which means that the change determination value ΔV is larger than the change threshold ΔVth, then the routine goes to the step 200 in which the in the step 150 obtained azimuth data are determined as ineffective data, and proceeds to the step 210 continued. If alternatively in the step 190 the answer NO is obtained, then the routine goes directly to the step 210 continued.
  • In the step 210 the ID number i is incremented by one (1) to select a subsequent one of the monopulse range Mi.
  • The routine continues with the step 220 in which it is determined whether or not the ID number i is greater than seven (7), that is, a total number of monopulse areas Mi. If the answer is NO is obtained, which means that the azimuth data has not yet been obtained on all monopulse areas Mi, then the routine returns to the step 120 back. Alternatively, if the answer YES is obtained, meaning that the azimuth data has been collected with respect to all the monopulse areas Mi, then the routine goes to the step 230 in which, based on the azimuth data relating to the monopulse areas M1 to M7, the azimuth angles and the number of targets located in front of the radar-mounted vehicle are determined, and the relative speed of the radar-equipped vehicle and the distance to each Targets are calculated based on beat signal frequencies in the frequency modulated rise and fall ranges using the known FM-CW radar techniques.
  • From the above discussion it follows that the radar device 2 of this embodiment, the monopulse regions M1 to M7 are defined to allow adjacent automobiles to be discriminated from each other via the radar detection zone. In particular, when two automobiles drive in front of the radar-mounted vehicle, one of them is always detected with a high signal level, thereby making it possible to discriminate between the two automobiles.
  • If, for example, as in 4 Target automobiles ➀ and ➁ traveling side by side are detected within a range of the monopulse regions M1 to M4, an echo of a radar wave from one of the automobiles ➀ and ➁ having a higher signal level than that of the other automobile in each of the monopulse regions M1 and M4 is detected on both sides of the area so that the azimuth angles of the automobiles ➀ and ➁ are accurately measured. In each of the central monopulse areas M2 and M3, the echoes of the radar wave are detected by the automobiles ➀ and ➁ with approximately equal signal levels, which results in a change in the azimuth angle thereof. The degree of this change is expressed in the change determination value ΔV and compared with the change threshold ΔVth to select the azimuth data obtained only in the monopulse regions M1 and M4 in which the time-sequential change of the azimuth data is small. This improves the accuracy of determining the azimuth of a target object and avoids unwanted control using incorrect azimuth data representing a larger time-sequential change, resulting in much improved control reliability. When a monopulse region having unstable azimuth data (ie, data whose change is large) exists between a pair of monopulse regions which generate stable azimuth data, the radar apparatus can 2 determine that two or more automobiles within an angular range travel over the monopulse ranges that produce the stable azimuth data, and may prevent determination of the azimuth of the targets. This is effective, especially in a case where there are three or more lanes on the road.
  • This embodiment uses, but is not limited to, eight receive antennas AR1 to AR8. Any number of receiving antennas greater than two may be used as long as a plurality of monopulse areas are provided in the radar detection zone.
  • Further, a known scanning mechanism that has been construed to swivel the receiving antennas while maintaining a preselected positional relationship therebetween to scan a monopulse range over the radar detection zone allows the number of chillers used in each of the first and second channels ch1 and ch2 to be measured Receive antennas is reduced by one. In particular, a single monopulse area formed by a pair of receiving antennas may be panned across the radar detection zone using the main scanning mechanism.
  • 5 represents a radar device 2a the second embodiment of the invention.
  • The radar device 2a contains an eight-channel receiver 6a , an A / D converter circuit 8a and a microcomputer 10a , The receiving antennas AR1 to AR8 have substantially the same directivity and cover the entirety of the radar detection zone. Other arrangements are identical to those of the first embodiment, and a detailed explanation thereof will be omitted here.
  • The recipient 6a consists of eight mixers MX1 to MX8 and eight amplifiers AMP1 to AMP8, which according to the figures are connected to the receiving antennas AR1 to AR8 in order to process input signals Sr1 to Sr8 to produce beat signals B1 to B8 of the A / D respectively. converter circuit 8a provide. Each of the amplifiers AMP1 to AMP8 removes unwanted components from one of the outputs of the mixers MX1 to MX8 as in the first embodiment.
  • The A / D converter circuit 8a consists of eight A / D converters AD1 to AD8 which sample the beat signals D1 to B8 to respectively generate digital data (ie, samples) D1 to D8. The microcomputer 10a performs a given operation on the samples as described later D1 to D8, which from the A / D converter circuit 8a be entered.
  • A combination of one of the mixers MX1 to MX8, the amplifiers AMP1 to AMP8, and one of the A / D converters AD1 to AD8 constitute a receiving channel. As clearly shown in the figures, these embodiments 8th Reception channels ready. In the following discussion, a receiving channel formed of the jth mixer MXj, the jth amplifier AMPj and the jth A / D converter ADj which receives the jth input signal Srj from the jth receiving antenna ARj treated, referred to as receiving channel chj.
  • The microcomputer 10a is formed of a CPU, a ROM and a RAM and has an input port in which data from the A / D converter circuit 8th and a digital signal processor (DSP) used in performing a fast Fourier transform (FFT). In particular, the microcomputer performs 10a In this embodiment, an operation of so-called beam forming, which will be described later, is performed on the samples D1 to D8.
  • In operation, when the radar wave in the form of a frequency modulated undamped wave (FM-CW) from the transmitting antenna AS of the transmitter 4 is sent and the antennas AR1 to AR8 of the receiver 6a each receiving an echo of the radar wave from an object within a radar detection zone, each receiving channel chj mixes, by the mixer MXj, the input signal Srj from the antenna ARj with that from the transmitter 4 supplied local signal L to generate the beat signal Bj, which is formed of a frequency component equivalent to a difference in frequency between the input signal Srj and the local signal L, amplifies and removes unwanted high frequency components from the beat signal Bj by the amplifier HMPj and converts the beat signal Bj by the A / D converter ADj in the digital beat signals Dj to. Each A / D converter ADj is designed to sample the beat signal Bj M-Mal (M = 512 in this embodiment) in each of the frequency-modulated rise and fall regions.
  • 6 shows a flowchart of a by the microcomputer 10a program to determine the azimuth of a target object using the digital beamforming technique. This program is executed every time the A / D converter circuit 8a stores the samples D1 to D8 obtained in all the reception channels ch1 to ch8 for one cycle of frequency changes in the transmission signal Ss.
  • After the program has entered, the routine goes to the step 310 in which a complex Fourier operation is performed using the FFT techniques with respect to each set of eight samples D1 to D8 which are sampled simultaneously in all receive channels ch1 to ch8, also below as a space or interval series -FFT operation (space series FFT operation). Specifically, twenty-four dummy data of zero (0) is added to the eight samples to perform a 32-point FFT operation, forming 32 beams defining thirty-one partially overlapping beams or monopulse ranges M1 to M31. Similar to the first embodiment, the distance between two adjacent receiving antennas AR1 to AR8 is determined such that the interval between the adjacent monopulse areas is set within a range which enables the juxtaposed automobiles to be accurately discriminated from each other.
  • The program moves to the step 320 in which the time series FFT operation with respect to each of the steps in the step 310 Thirty-two beams are taken to analyze the frequency thereof in each of the frequency modulated rise and fall ranges.
  • The routine continues with the step 330 Next, the ID number i is initialized to identify one of the monopulse areas Mi at one (1).
  • The routine continues with the step 340 in which the peak of the frequency components of each of the paired beams for forming the monopulse range Mi (that is, the monopulse range M1 in the first program cycle) is calculated on the basis of the results of the time series FFT operation. operation) in the step 320 is determined.
  • The routine continues with the step 340 Next, in which the frequency components of the adjacent beams forming the monopulse region Mi are grouped according to the frequency, a phase difference or an amplitude difference between the frequency components in each group is determined.
  • The following steps 350 to 440 are essentially identical to the steps 140 to 230 from 3 with the exception of step 430 in which it is determined whether the ID number i is greater than is thirty-one (31), that is, a total of the monopulse areas M1 to M31.
  • When two automobiles move side by side within the monopulse ranges M1 to M31, the radar detects 2a similar to the first embodiment, always one of them having a higher signal level, thereby making it possible to discriminate levels between two automobiles with high reliability.
  • The radar device described above 2a is constructed such that the space-series FFT operation is performed on 32 samples including dummys to form 32 beams logically defining the 31 monopulse areas M1 to M31 to obtain azimuth data with respect to each of the monopulse areas M1 to M31; thereby allowing an update cycle of the azimuth data to be shortened and improving the accuracy of various controls using the azimuth data of a target.
  • The time series FFT operation may alternatively be performed before the space series FFT operation. In this case, the time series FFT operation is performed on each of the samples D1 to D8. From the results of the time series FFT operation, positive frequency components and negative frequency components have exactly the same information. The subsequent space series FFT operation can thus be performed with respect to only one of the positive and negative frequency components, thereby reducing the operating load of the microcomputer 10a is greatly reduced.
  • The eight receiving channels ch1 to ch8 may be divided into a first serial channel handling the input signals Sr1 to Sr7 from the receiving antennas AR1 to AR7 other than the outermost receiving antenna AR8, and a second serial channel receiving the input signals Sr2 to Sr8 from the receiving antennas AR2 to AR8 outermost receiving antenna AR1 for performing the space-series FFT operation on data in the first and second serial channels, respectively, are split to form two series of digital beams. In this case, it is possible to form as many monopulse regions as there are beams provided in each of the first and second series channels.
  • For example, a plurality of the groups each formed of three adjacent beams may be formed into monopulse areas using a mixture of the left and center beams and a mixture of the right and center beams in each Define group.
  • The number of receiving antennas used in this embodiment may be two or more. In a case where the dummy data is not the samples are added when the FFT operation, it is recommended that the number of receive antennas for carrying out the space series FFT operation 2 n (n is a positive integer) is. In a case where the dummy data is added to the samples in the space series FFT operation, it is recommended that a total number of the receiving antennas and the dummy data be 2 n .
  • The antenna device 2a Alternatively, this embodiment may be formed to include a so-called phased array antenna structure which includes phase shifters which change the phase of the antenna outputs to the direction of the antenna outputs and an adder which outputs the phase shifters to form the so-called digital beams added together.
  • An explanatory example will be described below and differs from the first embodiment only in the location of the monopulse areas M1 to M7 defined by the receiving antennas AR1 to AR8 and a part of that of the microcomputer 10 performed azimuth determination operation. Other arrangements and operations are identical, and a detailed discussion will be omitted here.
  • The receiving antennas AR1 to AR8 are arranged such that, as in one example of FIG 15 (a) shown, two adjacent monopulse regions M1 to M7 with each other to three quarters (3/4) overlap. In the example of 15 (a) For example, it is possible to detect a target in at least three consecutive monopulse regions in a wide range from M3 to M7.
  • 7 FIG. 10 illustrates the azimuth determination operation of this example, which is similar to the first embodiment of the microcomputer 10 is performed every time the A / D converter circuit 8th stores the samples D1 and D2 produced by sampling the beat signals Bj for one cycle of the frequency changes in the transmission signal Ss formed by the input signals Srj obtained from echoes of a radar wave from all seven monopulse regions M1 to M7.
  • At the beginning of the azimuth determination operation, the routine goes to the step 510 in which an ID number i is used to identify one of the monopulse areas Mi and an ID number j for identifying one of the azimuth data groups GRj, as described later, to one (1).
  • The following steps 520 to 550 are identical to the steps 120 to 150 in the first embodiment. Specifically, the time series FFT operation is performed on each series of samples D1 and D2 obtained in one cycle of frequency changes in the transmission signal Ss from the input signals Srj included in the first and second channels ch1 and ch2 (step 520 ) are formed. The results of the time series FFT operation are analyzed to determine the frequency of the beat signal Bj and the phase or amplitude (ie, signal strength) of a frequency component of the beat signal Bj in each of the rise and fall regions of the modulated frequency (step 530 ). The frequency components in the first and second channels ch1 and ch2 are grouped according to the frequency, and a phase difference or an amplitude difference between the frequency components in each group is determined (step 540 ).
  • The azimuth data θ1 indicating the azimuth or the angular direction of the target object is determined on the basis of the phase or amplitude differences (step 550 ).
  • The following steps 560 to 590 group the azimuth data 91 which in the step 550 be won. In particular, in the step 560 determines whether the ID number i of the monopulse range is one or not. If the answer is YES, the routine goes directly to the step 590 continued. Alternatively, if the answer NO is obtained, the routine goes to the step 570 in which it is determined whether an absolute value of a difference between the azimuth data θi-1 obtained in the step 550 one program cycle earlier, and the azimuth data θi obtained in the step 550 in this program cycle is less than a preselected threshold θth or not. If the answer is YES, the routine goes to the step 590 continued. Alternatively, if the answer NO is obtained, the routine goes to the step 580 continues, in which the group ID number j is incremented by one.
  • The program moves to the step 590 in which the azimuth data θ i, which in step 550 are added to the azimuth data group GPj. More specifically, when the azimuth data θ1-1 obtained one program cycle earlier is compared with the azimuth data θi obtained in this program cycle, and when it is determined that they are both very close to each other, the azimuth data becomes θ1 and θ1-1 stored as falling in the same azimuth data group GP. Alternatively, if it is determined that the azimuth data is θ1 and θ1-1. are not close to each other, they are stored as belonging to different azimuth data groups GP.
  • The following steps 600 and 610 are identical to the steps 210 and 220 , In particular, in the step 600 the ID number i is incremented by one (1) to select a subsequent one of the monopulse areas Mi. In the step 610 It is determined whether or not the ID number i is greater than seven (7), that is, a total number of the monopulse areas Mi. If the answer NO is obtained, which means that the azimuth data with respect to all the monopulse areas Mi has not yet been obtained, then returns the routine to the step 520 back. Alternatively, if a YES answer is obtained, meaning that the azimuth data has been collected with respect to all the monopulse areas Mi, then the routine goes to the step 620 continued.
  • In the step 620 the group ID number j is stored as the number Ngp of the azimuth data groups GP and is initialized to one again. The routine continues with the step 630 in which it is determined whether or not the number of data contained in the azimuth data group GPj is one or not. If a NO answer is obtained, then the routine goes directly to the step 650 continued. Alternatively, if the answer is YES, then the routine goes to the step 640 in which the data in the azimuth data group GPj is determined to be an ineffective value. The routine continues with the step 650 continues, in which the group ID number j is increased by one (1). The routine continues with the step 660 in which it is determined whether or not the group ID number j is greater than the azimuth data group number Ngp. If the answer is NO, the routine returns to the step 630 back. Alternatively, if the answer YES is obtained, meaning that the above operations have been performed on all the azimuth data groups GP, then the routine goes to the step 670 in which the azimuth data obtained by radar echoes from all monopulse regions M1 to M7 and as rms values in the step 630 can be used to determine the azimuth angles and the number of target objects present in front of the radar-mounted vehicle, and the relative velocity of the radar-equipped vehicle and the distance to each target are determined based on beat signal frequencies in the frequency modulated rise and fall ranges using the known FM-CW radar techniques.
  • For example, if target vehicles ➀ and ➁, which, as in 8th are shown side by side at an interval away from each other, are detected within a range of the monopulse regions M1 to M7, the azimuth data obtained from the monopulse regions M1 to M3 are added to the azimuth data group GP1, the azimuth data obtained from the monopulse region M4 are added to the azimuth data group GP2 For example, the azimuth data obtained from the monopulse area M5 is added to the azimuth data group GP3, and the azimuth data obtained from the monopulse areas M6 and M7 are added to the azimuth data group GP4. In this case, only the azimuth data belonging to the azimuth data groups GP1 and GP4 are determined as close to each RMS values. Specifically, the azimuth of the target automobile ➀ is calculated using the data in the azimuth data group GP1, while the azimuth of the target automobile ➁ is calculated using the data in the azimuth data group GP2.
  • As described above, this explanatory example defines the monopulse regions M1 to M7 such that three quarters of two adjacent ones thereof overlap. This enables even when target automobiles travel side by side in front of the radar-mounted vehicle, a plurality of monopulse ranges are always provided which can be used to accurately determine the azimuth of each of the targets.
  • The third embodiment of the invention will be described below and differs from the above illustrative example 7 and 8th only in part of the microcomputer 10 performed azimuth determination operation. Other arrangements and operations are identical, and a detailed explanation thereof will be omitted here.
  • 9 Fig. 10 shows the azimuth determination operation of the third embodiment. The steps 710 to 820 are identical to the steps 510 to 620 , Following steps 830 to 870 are identical to the steps 160 to 200 at the in 3 illustrated first embodiment. In particular, in the step 830 performing an identity check operation for determining whether or not the target object detected in this program cycle based on the data in the azimuth data group GPj is identical to one detected in a previous program cycle based on data in the azimuth data group GPj. The routine continues with the step 840 in which the results of the surgery in the step 830 to determine if the target object detected in this program cycle is a new one or not. If the answer is YES, then the routine goes directly to the step 880 continued. Alternatively, if the answer NO is obtained, meaning that the target object detected in this program cycle is identical to one detected in the previous program cycle, then the routine goes to the step 850 Next, in which a change determination value .DELTA.V for determining a time-sequential change in the thus obtained azimuth data is calculated. The routine continues with the step 860 in which it is determined whether or not the change determination value ΔV is larger than a change threshold ΔVth. If the answer is YES, meaning that the change determination value ΔV is greater than the change threshold ΔVth, then the routine goes to the step 870 continued. Alternatively, if the answer NO is obtained, thereafter the routine goes directly to the step 880 continued.
  • The identity checking operation is performed similarly to the first embodiment by comparing the frequencies of the beat signals used in determining the azimuth data. When a plurality of azimuth data are included in each azimuth data group GPj, a representative value of the azimuth data (for example, an average value or a central value) for the frequency comparison is determined.
  • In the step 880 the group ID number j is incremented by one (1). The routine continues with the step 890 in which it is determined whether or not the group ID number j is larger than the azimuth data group number Ngp. If the answer is NO, then the routine returns to the step 830 back. Alternatively, if the answer YES is obtained, meaning that the above operations have been performed on all the azimuth data groups GP, then the routine goes to the step 900 in which the azimuth data obtained by radar echoes from all monopulse regions M1 to M7 and as effective values in the step 870 can be used to determine the azimuth angles and the number of targets in front of the radar-mounted vehicle, and the relative velocity of the radar-mounted vehicle and the distance to each target are determined based on beat signal frequencies in the frequency modulated rise and fall regions using the known FM-CW radar techniques.
  • For example, if target automobiles ➀ and ➁, which, as in 10 are displayed in a range of the monopulse regions M1 to M7, the azimuth data obtained from the monopulse regions M1 to M3 are added to the azimuth data group GP1, the azimuth data obtained from the monopulse region M4 is added to the azimuth data group GP2 the azimuth data obtained from the monopulse area M5 are added to the azimuth data group GP3, and the azimuth data obtained from the monopulse areas M6 and M7 are added to the azimuth data group GP4. In this case, only the azimuth data belonging to the azimuth data groups GP1 and GP4 are determined as close to each other effective values. Specifically, the azimuth of the target automobile ➀ is calculated using the data in the azimuth data group GP1, while the azimuth of the target automobile ➁ is calculated using the data in the azimuth data group GP4.
  • The third embodiment also performs the time-sequential change determination operation on the azimuth data group GP included in individual data, but can do it only with respect to the azimuth data groups GP each contained in a plurality of the azimuth data. This reduces the load on the microcomputer 10 operational.
  • The above illustrative example according to FIG 7 and 8th and the third embodiment define monopulse regions M1 to M7 such that three quarters of two adjacent ones thereof overlap each other, however, the monopulse regions M1 to M7 may be as shown in FIG 15 (b) are formed such that one-half of two adjacent ones thereof overlap each other and one half of the width of each monopulse area Mi is smaller than the width of a target object. This enables, similar to the above embodiments, effective azimuth data to always be obtained in two or more monopulse areas. The size of overlapping portions of the monopulse areas is not limited as long as they are larger than one-half of each monopulse area.
  • The above illustrative example according to FIG 7 and 8th and the third embodiment have been described as modifications of the first embodiment, but they may use the structure of the second embodiment which forms beams using the DBF techniques.

Claims (6)

  1. Radar device with: a transmitter ( 4 ) which sends a radar wave; a signal receiver ( 6 ) having antennas (AR1-AR8) which form overlapping antenna lobes to define monopulse regions, the signal receiver (AR) 6 ) is adapted to receive an echo of the radar wave from a target object in the monopulse regions to produce a pair of input signals; an angular direction data determining circuit ( 10 ) configured to process the per-monopulse range generated pair of input signals to obtain angular direction data in a time sequence each indicative of an angular direction of the target based on amplitude or phase differences between the two input signals per monopulse range; and a change determination circuit ( 10 ), which is adapted to determine a change in the angular direction data obtained in a time sequence in each of the monopulse areas, and the angular direction data whose change is within a preselected permissible range, determined as values used in determining a Angular direction of the target object are valid.
  2. Radar apparatus according to claim 1, characterized in that the signal receiver ( 6 ) is formed such that the antenna lobes formed by the antennas (AR1-AR8) are such that two adjacent monopulse regions partially overlap.
  3. Radar apparatus according to claim 1, characterized in that the signal receiver ( 6 ) includes three or more antennas (AR1-AR8) located such that the antenna lobes are respectively aligned in different directions and that two adjacent antenna lobes define one of the monopulse regions.
  4. Radar apparatus according to claim 1, characterized in that the signal receiver ( 6 ) a plurality of antennas (AR1-AR8) arranged in a line so that the antenna lobes thereof are aligned in the same direction, and a signal processing circuit which generates outputs from the antennas (AR1-AR8) with a given weighting the antenna lobes summed.
  5. Radar apparatus according to claim 4, characterized in that the signal processing circuit comprises an analog-to-digital converter ( 8th ) which is designed such that it outputs from the antennas (AR1-AR8) of the signal receiver ( 6 ) to generate digital signals and an arithmetic circuit ( 10 ) configured to perform a complex Fourier transform on the digital signals in a pitch series along an array of the antennas (AR1-AR8).
  6. Radar apparatus according to claim 5, characterized in that the arithmetic circuit ( 10 ) like this is configured to receive zero dumb signals from the analog-to-digital converter ( 8th ) in such a way that the number of signals simultaneously subjected to the complex Fourier transformation is greater than the number of outputs from the antennas (AR1-AR8) of the signal receiver ( 6 ).
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US6337656B1 (en) 2002-01-08

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